Fish barriers should consist of oonorete dams 10 to 15 feet 

 high, with long, shallow aprons. They should be equipped with high 

 standard fish ladders adapted for ease in counting the fish passing 

 over them. "Phe ladders should also be fitted with effective closing 

 devices. The barriers should be strong enough to withstand floods 

 which might be anticipated following construction of the dams and should 

 be located where spawning areas are restricted and where a minimum of 

 gravel will be inundated by their forebays. 



3. The flow could be regulated to produce only the ario\mt of 

 spawning area needed each year, depending on the number of migran'ts . — 

 Regulation of the flow to approximate the needs of migratory fishes 

 on an annual basis would require reservoir operation similar to that 

 in type 2, but with variable spawning flows. Regulation of the spawning 

 flow each year to meet needs of the particular salmon population would 

 be more expensive to operate than other plans. It would call for the 

 construction of an additional fish block and counting structure near 

 the North Fork of Trinity River that would of necessity be sufficiently 

 massive to withstand any floods that might occur* 



fhe plan for eaoh year would be based on counts by resident 

 biologists of migrating salmon and stealhead made as they passed 

 North Fork, which is prestnnably far enough downstream to allow flow 

 schedule determination prior to the aottial need* This system could 

 be hazardous for the salmon, as their migration past North Fork may 

 not be completed before the peak spawning period starts below Lewis ton. 

 Lake segments of the runs may not find sufficient gravel for their needs. 

 Flow changes should be made at weekly intervals starting October 15, and 

 the revisions should be determined by the cumulative counts obtained at 

 the oo\inting station near North Fork. The flow would be increased in 

 accordance with the need for additional nesting capacity between Lewiston 

 dam and North Fork as determined from Table 21* This plan would utilize 

 both water flow and spawning areas most effectively* 



Probable water requirements for this plan, had it been in operation 

 during 1944 and 1945, are given in Table 22, Ihe peak spawning period 

 would have required a release of 280 cubic feet per second in 1944, and 

 250 in 1945* These flows are conservative as they only provide additional 

 spawning area for the number of salmon acttially counted at Lewiston, and 

 do not provide for salmon passing Lewiston before and after the counting 

 period* The spawning flows given in Table 22 were determined by adding 

 the number of nests needed for counted fish to the number of nests 

 •normally occupied in the spawning area (5,647)* The spawning population 

 passing Lewiston required 3,774 nests in 1944, and 2,856 in 1945, The 

 flow producing the total number of nests was chosen to the nearest 10 

 cubic feet per second from Table 21* 



63 



